dotnet/efcore · error · InvalidOperationException

A seed entity for entity type

Error message

A seed entity for entity type '{entityType}' has the same key value {keyValue} as another seed entity mapped to the same table '{table}'. Key values should be unique across seed entities.

What it means

During migration diffing, EF builds an identity map keyed by primary key per target table. For a non-shared table, encountering two seed entities with the same key is ambiguous and throws DuplicateSeedData, because the diff could not decide which seed wins.

Solutions

Dedupe seed data: ensure each key value appears exactly once per entity type per table.
When merging seeds from multiple modules, run a union/dedup pass keyed by primary key before HasData.
Enable sensitive data logging to see the offending key value (DuplicateSeedDataSensitive message includes it).
Re-run Add-Migration after correcting the seed data so the diff is regenerated.

Example fix

// before
modelBuilder.Entity<User>().HasData(
    new User { Id = 1, Name = "Alice" },
    new User { Id = 1, Name = "Bob" }); // duplicate key 1

// after
modelBuilder.Entity<User>().HasData(
    new User { Id = 1, Name = "Alice" },
    new User { Id = 2, Name = "Bob" });

Defensive patterns

Strategy: validation

Validate before calling

// Dedupe seed data by primary key before calling HasData.
var deduped = seedUsers
    .GroupBy(u => u.Id)
    .Select(g => g.First())
    .ToArray();
modelBuilder.Entity<User>().HasData(deduped);

Type guard

static bool HasUniqueKeys<T, TKey>(IEnumerable<T> rows, Func<T, TKey> keySelector)
    => rows.GroupBy(keySelector).All(g => g.Count() == 1);

Prevention

Dedupe seed collections by key before HasData.
Enable sensitive data logging during development to surface the colliding key value.
Merge seeds from multiple modules with a union-by-key step.

When it happens

Trigger: Two HasData calls (or one with two objects) seeding the same entity type with identical key values, both mapped to the same non-shared table; or re-seeding after a key change left duplicates.

Common situations: Copy-pasted seed rows; merging seed data from multiple configuration sources; key generators producing collisions; version upgrades that changed key computation (value converters) so previously-distinct seeds now collide.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/4815c2649fd40acf. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Relational/Migrations/Internal/MigrationsModelDiffer.cs:1929

                    var valueConverter = columnMapping.TypeMapping.Converter;
                    key[i] = NormalizeSeedValue(
                        valueConverter == null
                            ? value
                            : valueConverter.ConvertToProvider(value));
                }

                if (!keyFound)
                {
                    continue;
                }

                if (identityMap.FindCommand(key) is { } existingCommand)
                {
                    if (!table.IsShared)
                    {
                        if (sensitiveLoggingEnabled)
                        {
                            throw new InvalidOperationException(
                                RelationalStrings.DuplicateSeedDataSensitive(
                                    entityType.DisplayName(),
                                    BuildValuesString(key),
                                    table.SchemaQualifiedName));
                        }

                        throw new InvalidOperationException(
                            RelationalStrings.DuplicateSeedData(
                                entityType.DisplayName(),
                                table.SchemaQualifiedName));
                    }

                    command = existingCommand;
                }
                else
                {
                    command = CommandBatchPreparerDependencies.ModificationCommandFactory.CreateNonTrackedModificationCommand(
                        new NonTrackedModificationCommandParameters(table, sensitiveLoggingEnabled));

View on GitHub (pinned to 3a2006ef56)